seasonal variation: Rainfall may be distributed evenly throughout the year or be marked by seasonal variations.

dry summer, wet winter: Most regions of the earth receive most of their rainfall during the summer months; Mediterranean climate regions receive their rainfall during the winter months.

Elevation: Increasing elevation causes a distribution of habitat types similar to that of increasing latitude.

The most widely used systems of classifying biomes correspond to latitude (or temperature zoning) and humidity. Biodiversity generally increases away from the poles towards the equator and increases with humidity.

Biomes are classification schemes defined by climatic parameters. Particularly in the 1970s and 1980s, there was a significant push to understand the relationships between these climatic parameters and properties of ecosystem energetics because such discoveries would enable the prediction of rates of energy capture and transfer among components within ecosystems. Such a study was conducted by Sims et al. (1978) on North American grasslands. The study found a positive logistic correlation between evapotranspiration in mm/yr and above-ground net primary production in g/m2/yr. More general results from the study were that precipitation and water use led to above-ground primary production, solar radiation and temperature lead to below-ground primary production (roots), and temperature and water lead to cool and warm season growth habit.[4] These findings help explain the categories used in Holdridge’s bioclassification scheme (see below), which were then later simplified in Whittaker’s (see below). The number of classification schemes and the variety of determinants used in those schemes, however, should be taken as strong indicators that biomes do not all fit perfectly into the classification schemes created.

In this scheme, climates are classified based on the biological effects of temperature and rainfall on vegetation under the assumption that these two abiotic factors are the largest determinants of the type of vegetation found in an area. Holdridge uses the four axes to define 30 so-called "humidity provinces", which are clearly visible in the Holdridge diagram. While his scheme largely ignores soil and sun exposure, Holdridge did acknowledge that these, too, were important factors in biome determination.

The distribution of vegetation types as a function of mean annual temperature and precipitation.

Whittaker appreciated biome-types as a representation of the great diversity of the living world, and saw the need to establish a simple way to classify them. He based his classification scheme on two abiotic factors: precipitation and temperature. His scheme can be seen as a simplification of Holdridge's, one more readily accessible, but perhaps missing the greater specificity that Holdridge's provides.

Whittaker based his representation of global biomes on both previous theoretical assertions and an ever-increasing empirical sampling of global ecosystems. He was in a unique position to make such a holistic assertion because he had previously compiled a review of biome classification.[5]

Physiognomy: The apparent characteristics, outward features, or appearance of ecological communities or species

Biome: a grouping of terrestrial ecosystems on a given continent that are similar in vegetation structure, physiognomy, features of the environment and characteristics of their animal communities

Formation: a major kind of community of plants on a given continent

Biome-type: grouping of convergent biomes or formations of different continents, defined by physiognomy

Formation-type: a grouping of convergent formations

Whittaker's distinction between biome and formation can be simplified: formation is used when applied to plant communities only, while biome is used when concerned with both plants and animals. Whittaker's convention of biome-type or formation-type is simply a broader method to categorize similar communities.[6]

Whittaker, seeing the need for a simpler way to express the relationship of community structure to the environment, used what he called "gradient analysis" of ecocline patterns to relate communities to climate on a worldwide scale. Whittaker considered four main ecoclines in the terrestrial realm.[6]

Intertidal levels: The wetness gradient of areas that are exposed to alternating water and dryness with intensities that vary by location from high to low tide

Climatic moisture gradient

Temperature gradient by altitude

Temperature gradient by latitude

Along these gradients, Whittaker noted several trends that allowed him to qualitatively establish biome-types.

The gradient runs from favorable to extreme, with corresponding changes in productivity.

Changes in physiognomic complexity vary with the favorability of the environment (decreasing community structure and reduction of stratal differentiation as the environment becomes less favorable).

Trends in diversity of structure follow trends in species diversity; alpha and beta species diversities decrease from favorable to extreme environments.

Each growth-form (i.e. grasses, shrubs, etc.) has its characteristic place of maximum importance along the ecoclines.

The same growth forms may be dominant in similar environments in widely different parts of the world.

Whittaker summed the effects of gradients (3) and (4) to get an overall temperature gradient, and combined this with gradient (2), the moisture gradient, to express the above conclusions in what is known as the Whittaker classification scheme. The scheme graphs average annual precipitation (x-axis) versus average annual temperature (y-axis) to classify biome-types.

The Heinrich Walter classification scheme, developed by Heinrich Walter, a German ecologist, differs from both the Whittaker and Holdridge schemes because it takes into account the seasonality of temperature and precipitation. The system, also based on precipitation and temperature, finds 9 major biomes, with the important climate traits and vegetation types summarized in the accompanying table. The boundaries of each biome correlate to the conditions of moisture and cold stress that are strong determinants of plant form, and therefore the vegetation that defines the region. Extreme conditions, such as flooding in a swamp, can create different kinds of communities within the same biome.

Robert G. Bailey almost developed a biogeographical classification system for the United States in a map published in 1976. He subsequently expanded the system to include the rest of North America in 1981, and the world in 1989. The Bailey system, based on climate, is divided into seven domains (polar, humid temperate, dry, humid, and humid tropical), with further divisions based on other climate characteristics (subarctic, warm temperate, hot temperate, and subtropical; marine and continental; lowland and mountain).[7]

A team of biologists convened by the World Wide Fund for Nature (WWF) developed an ecological land classification system that identified fourteen biomes,[8] called major habitat types, and further divided the world's land area into 882 terrestrial ecoregions(includes new Antarctic ecoregions by Terrauds et al. 2012). Each terrestrial ecoregion has a specific EcoID, format XXnnNN (XX is the ecozone, nn is the biome number, NN is the individual number). This classification is used to define the Global 200 list of ecoregions identified by the WWF as priorities for conservation. The WWF major habitat types are:

Humans have altered global patterns of biodiversity and ecosystem processes. As a result, vegetation forms predicted by conventional biome systems can no longer be observed across much of Earth's land surface as they have been replaced by crop and rangelands or cities. Anthropogenic biomes provide an alternative view of the terrestrial biosphere based on global patterns of sustained direct human interaction with ecosystems, including agriculture, human settlements, urbanization, forestry and other uses of land. Anthropogenic biomes offer a new way forward in ecology and conservation by recognizing the irreversible coupling of human and ecological systems at global scales and moving us toward an understanding of how best to live in and manage our biosphere and the anthropogenic biomes we live in.

The endolithic biome, consisting entirely of microscopic life in rock pores and cracks, kilometers beneath the surface, has only recently been discovered, and does not fit well into most classification schemes.

This "see also" section may contain an excessive number of suggestions. Please ensure that only the most relevant suggestions are given and that they are not red links, and consider integrating suggestions into the article itself. (June 2013)

UCMP Berkeley's The World's Biomes – provides lists of characteristics for some biomes and measurements of climate statistics.

Gale/Cengage has an excellent Biome Overview of terrestrial, aquatic, and man-made biomes with a particular focus on trees native to each, and has detailed descriptions of desert, rain forest, and wetland biomes.

NASA's Earth Observatory Mission: Biomes gives an exemplar of each biome that is described in detail and provides scientific measurements of the climate statistics that define each biome.